The present invention relates to a method and an apparatus for edge shaping in a high-pressure fuel reservoir.
A high-pressure fuel reservoir for a fuel injection system for internal combustion engines is presented, for example, in German Published Patent Application No. 196 40 480. This reference discloses an elongated tubular casing element made of steel which can be connected to a high-pressure fuel pump. The casing element has a continuous recess which extends in the longitudinal direction, constitutes the interior space of the high-pressure fuel reservoir, and is open at at least one end. When the high-pressure fuel reservoir is in the completely installed state, the at least one open end is closed off by the connector of the high-pressure fuel pump or of a pressure-limiting valve, or in another manner. The fuel contained in the high-pressure fuel reservoir and impinged upon by high pressure is delivered, via multiple connectors configured in the casing element and high-pressure lines connected thereto, to electrically controlled injection valves (called xe2x80x9cinjectorsxe2x80x9d) for injection into the combustion chambers of a compression-ignited internal combustion engine. A high-pressure fuel reservoir of this kind is also called a xe2x80x9ccommon rail.xe2x80x9d The connectors of the high-pressure fuel reservoir are configured in the form of connector fittings which stand out from the casing element and are each equipped with a passthrough orifice, configured as a bore, that opens into the continuous recess of the casing element. The passthrough orifice forms a peripheral edge with the continuous recess. As a result of the high internal pressure (approximately 1350 bar) in the high-pressure fuel reservoir and because of the narrow diameter (a few millimeters) of the bores, abrasive particles in the fuel cause wear phenomena in the region of the peripheral edge formed by the passthrough orifice and the inner wall of the continuous recess. For this reason, it is desirable to round off or smooth the edge contour. It is known to shape and round off the edge contour using methods such as, for example, honing, in which an abrasive paste is used. These methods are, however, relatively cumbersome and very complex.
The method according to the present invention makes it possible to greatly reduce the effort necessary for smoothing the edge contour. The method can be performed very economically and inexpensively, and uses a pressure element that is pressed, by an actuation element introduced into the continuous recess, against the peripheral edge in such a way that smoothing of the edge contour is achieved by material displacement in the region of the edge. The modification of the edge contour advantageously contributes to an increase in material strength. As a result, cracks, fractures, and particle detachments occur much less frequently on the rounded edge that has been consolidated with respect to the fuel flow.
It is furthermore advantageous if a guide element, in which the pressure element is mounted movably perpendicularly to the longitudinal axis of the continuous recess, is used to guide the pressure element. Using the guide element, a force acting on the actuation element in the insertion direction of the actuation element is deflected in enhanced fashion perpendicularly to the longitudinal axis of the continuous recess, and acts substantially in that direction on the edge of the high-pressure fuel reservoir that is to be shaped.
Advantageously, the guide element is initially arranged shiftably in the continuous recess, so that upon contact by the pressure element against the peripheral edge, the guide element is shifted in the continuous recess until the pressure element is arranged centeredly with respect to the continuous recess. The guide element can then be immobilized with respect to the high-pressure fuel reservoir, and the edge contour can be shaped by pressure of the pressure element.
It is particularly advantageous if a ball whose diameter is greater than the inside diameter of the passthrough orifice is used as the pressure element. A ball is particularly easy to manufacture with the necessary precision and possesses great mechanical stability, so that a ball is particularly suitable as a pressure element. The spherical shape of the ball surface is particularly suitable for shaping the edge contour.
Any drilling burr that may be present on the edge formed by the continuous recess and the passthrough orifice is advantageously removed before the pressure element is pressed on, since the presence of a drilling burr can greatly impair smoothing of the edge contour. The method described in German Published Patent Application No. 100 01 507, for example, can be used to remove a burr.
Also provided is an apparatus for edge shaping in a high-pressure fuel reservoir which has an elongated tubular casing element that is equipped in the longitudinal direction with a continuous recess which forms the interior space of the high-pressure fuel reservoir and is open at at least one end. The at least one end opens into at least one passthrough orifice, configured as a bore, that with the continuous recess forms a peripheral edge. The apparatus includes: an elongated casing-shaped guide element that is insertable into the continuous recess, having a recess extending in the longitudinal direction of the guide element and an orifice branching off from the recess perpendicularly to the longitudinal direction; a pressure element mounted movably in the orifice; and an actuation element. The actuation element acts with the pressure element and is arranged shiftably in the recess, and is equipped at its end inserted into the recess with a surface segment that is inclined at an angle with respect to the longitudinal direction of the guide element and is in contact against the pressure element. In this context, the pressure element can, by introduction of the actuation element into the guide element, be impinged upon by a force, and consequently push out with a surface portion through the orifice of the guide element in order to shape the edge of the high-pressure fuel reservoir.
Advantageously, the actuation element is arranged in slidingly shiftable fashion in the recess of the guide element, and is of wedge-shaped configuration at its end inserted into the recess.
The orifice in the casing-shaped guide element can be configured simply as a radial bore.
It is particularly advantageous if the pressure element makes contact against the inner wall of the orifice with a slight lateral clearance. This results in accurate guidance of the pressure element. The pressure element can advantageously be configured as a ball. The diameter of the ball is greater than the inside diameter of the passthrough orifice.